New function: ignore, synonym of nilf.

This will be an official mechanism for indicating
deliberately unused variables.

* eval.c (eval_init): Register ignore intrinsic,
binding to the same function object as nilf.

* stdlib/compiler.tl (%const-foldable-funs%): Mention
ignore function, next to its nilf synonym.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.

1 files changed, 6 insertions, 1 deletions

diff --git a/eval.c b/eval.c
index e09db92a..343ea49f 100644
--- a/eval.c
+++ b/eval.c
@@ -7160,7 +7160,12 @@ void eval_init(void)
   reg_fun(intern(lit("callf"), user_package), func_n1v(callf));
   reg_fun(intern(lit("mapf"), user_package), func_n1v(mapf));
   reg_fun(intern(lit("tf"), user_package), func_n0v(tf));
-  reg_fun(intern(lit("nilf"), user_package), func_n0v(nilf));
+
+  {
+    val nilf_f = func_n0v(nilf);
+    reg_fun(intern(lit("nilf"), user_package), nilf_f);
+    reg_fun(intern(lit("ignore"), user_package), nilf_f);
+  }
 
   reg_fun(intern(lit("print"), user_package), func_n3o(print, 1));
   reg_fun(intern(lit("pprint"), user_package), func_n2o(pprint, 1));